1. Field of the Invention
This invention relates to an improved method for regenerating of brine and more particularly, for the use of waste heat from a producing oil well to aid in the regeneration of the brine.
2. Description of the Prior Art
In many processes of softening hard water, the hard water, generally water having calcium and/or magnesium salts dissolved therein, is contacted with a strong acid ion exchange resin. Ion exchange resins can be minerals such as zeolite or, now more commonly, various synthetic resins. The resins soften the hard water by exchanging the calcium and/or magnesium ions for sodium and/or potassium ions. Softened hard water is desirable in many instances, since hard water produces undesirable results in many uses, such as forming scale or other deposits during the production of steam in a steam generating device. The sodium and potassium salts do not have the same effects and are not generally deleterious to devices or methods employing the softened water.
Once the ion exchange resin has been effectively depleted of sodium or potassium ions during the water softening process, the ion exchange resin is generally regenerated by contacting the exhausted ion exchange resin with brine. The sodium ions in the brine exchange for the calcium and/or magnesium ions of the exhausted ion exchange resin. This regenerates the ion exchange resin and permits the ion exchange resin to soften further quantities of hard water. Methods and apparatus for softening water and regenerating the ion exchange resin are set forth in many patents including U.S. Pat. Nos. 4,207,397; 3,899,421; and 3,616,912.
In many previously used water softening processes, the brine was simply disposed of after it had regenerated the ion exchange resin. However, this presents two problems, one is that when large quantities of ion exchange resin are to be regenerated, the cost of the brine increases greatly. Further, with environmental regulations, disposal of large quantities of brine is becoming more and more difficult and more and more expensive because of the deleterious effects of the brine both on soil and on local water supplies. For these reasons and others, attempts have been made to regenerate brine, generally, by removing the calcium and/or magnesium ions from the brine.
Representative chemical methods for precipitating out the calcium and/or magnesium ions from the used brine are set forth in U.S. Pat. Nos. 3,977,968 and 3,528,912. However, the use of chemicals to precipitate out calcium and/or magnesium ions requires the use of relatively expensive chemicals. There are also problems in removing the precipitate from the brine solution, and in disposing of the precipitated material.
Another problem in regenerating the brine used in a water softening system results from the fact that the brine is diluted during the regeneration of the strong acid ion exchange resin. The dilution of the brine generally results from the addition of water used to wash the strong acid ion exchange resin. The concentration of the sodium chloride in the diluted brine must be brought up to a desired concentration, preferably about 10 percent by weight, during any brine regeneration process.
One use for softened water is in the secondary recovery of oil. One method of recovering oil from underground reservoirs, which is not otherwise readily recovered, comprises drilling into the oil bearing formations and injecting steam into the formations. The steam heats the viscous oil, making it easier to bring the oil to the surface. A steam injection process for oil recovery is disclosed in U.S. Pat. Nos. 3,237,692 and 3,193,009.
Steam injection methods require large quantities of water. Boiling hard water to form steam results in many problems, such as the formation of scale in the boilers which is associated with the calcium and/or magnesium ions found in hard water. The large quantities of softened water required result in large quantities of brine being used to regenerate the resins which are used to soften the hard water.